In driver assistance systems for motor vehicles, for example, in ranging systems or collision warning systems, radar systems are used for sensing the surrounding field of traffic, in particular for locating the position of other traffic participants. Due to safety considerations, such radar sensors must be continually checked to ensure that the sensor is actually operational and, accordingly, whether the assistance function supported by the radar sensor is actually available and performing reliably. For this purpose, the self-monitoring device monitors various important operating parameters of the radar sensor.
The German Patent Application DE 199 45 250 A1 describes a radar sensor of this type where the self-monitoring device is used for recognizing a blinding of the radar sensor.
It has also been discussed to monitor other operating parameters, for example, the amplitudes or power levels of the transmitted radar signals, amplitude differences and phase differences among the signals in various transmit and receive channels, and the like. When the detected deviation between the setpoint and actual values for one of these parameters is outside of a permissible tolerance range, a self-deactivation of the radar sensor results, and a dashboard warning is issued to the motor vehicle driver indicating that the assistance function in question is not available.
Since driver assistance systems for motor vehicles are generally safety-related systems, only narrow tolerance limits are permissible for the important operating parameters of the radar sensor to ensure a proper operation thereof in all circumstances. However, the narrower the tolerance limits are, the more frequent are situations where an error signal is communicated to the driver. This can limit the acceptance of the driver assistance system.